In general, this invention relates to a process and an apparatus for producing magnetic recording media.
Several techniques are known for preparing magnetic recording media. Typically, they include applying a magnetic coating containing tiny magnetic particles uniformly dispersed in a curable binder on a tape or disk surface. For giving the particles a preferred directional orientation they are passed through a magnetic orienting field. Use of magnetic recording media is determined typically by the orientation of the magnetic particles. For permanently setting these particles in a desired orientation, the coating is dried or cured.
The most common orientation for such particles is to have their axes of easy magnetization arranged in end-to-end fashion along the longitudinal extent of a tape. While such conventional longitudinal recording orientations have served satisfactorily there are number of factors which limit recording density.
Some have suggested that conventional longitudinal-recording has already been pushed close to its ultimate ceiling. Examples of known techniques for achieving the foregoing kinds of orientation are illustrated and described in the following U.S. Pat. Nos. 2,711,901; 3,117,065; 3,437,514 and 3,775,178. It is also known to have the particles arranged so that their axes of easy magnetization are generally transversely oriented with respect to the longitudinal extent of the tape. Also, it is known that in the production of floppy disks, magnets are used to disorient particles which have become oriented by virtue of coating.
For purposes of enhancing the density packing of the particles so as to improve recording characteristics of recording media, it has been proposed to orient these particles in such a manner that their axes of easy magnetization are situated generally 90.degree. with respect to the tape surface. In other words, the particles are aligned generally perpendicularly with respect to the substrate surface they coat. By having them generally perpendicular, there is greater density of particles per unit area. Accordingly, more electronic information can be stored and read.
Previously referenced U.S. Pat. No. 2,711,401 also illustrates and describes a process, whereby the magnetic particles are oriented vertically with respect to the substrate. This is achieved under the influence of a magnetic field created by conventional permanent magnets spaced apart and having magnetically opposing poles facing each other. As the particles pass through this field in an uncured binder, they tend to rotate so that their easy axes align with the flux lines of such fields. Subsequently, the binder is cured for permanently setting the particles in this preferred orientation.
There is a drawback with the foregoing approaches in that these particles have a tendency to become quickly misaligned as they leave the orientation field and travel to the curing station. Moreover, the flux lines of these conventional permanent bar magnets are in a somewhat splayed relationship to one another.
Recently issued Japanese Patent Publication No. 55-163633(A) discloses a method of producing magnetic recording media having the particles aligned generally perpendicularly, while the coating is simulataneously air dried in the field. This approach has several shortcomings one of which being that it relies upon a conventional air drying technique which is considered too slow for commercial production.
Recently issued U.S. Pat. No. 4,407,853 describes a method, whereby electron beams irradiate a magnetic coating on a substrate for promoting rapid curing. Disclosed is, however, a preference for irradiating the layer subsequent to the magnetic orienting step, although simultaneous irradiating and orienting are mentioned. Besides however, the orienting techniques described generally make reference to using conventional, bar-type permanent magnets or electromagnets in a manner for effecting longitudinal orientation of the particles. Individual flux lines of these kinds of magnets tend to be in a somewhat splayed relationship to each other. Hence, the oriented particles would assume a generally splayed relationship. As noted, this relationship is less than ideal.
Beyond the foregoing disadvantages, none of the known techniques teaches minimizing chaining or roping of the particles subjected to the influence of a strong field. Chaining or roping tend to create surface imperfections on the recording media. Hence, a less desirable media is formed.